Graphic file types

There are many different graphic file types which you can save an image using. SOme provide better graphic quality than others as well as differing in file size.

1. GIF – GIF stands for Graphic Interchange Format it is a standard file format used World Wide. IT is most commonly used for animations rather than coloured photos as it only is capable of representing 256 colours. Unlike JPEG it uses lossless compression techniques meaning no quality is lost. This image is only 24.3kb in size due to its inability to store a vast range of colours

PNG – PNG stands for Portable Network Graphics. It is similar to GIF as it shares the ability to support transparency. PNG was seen as a more developed version of GIF and can be compressed up to 25% more although it cannot store animation. This PNG image is 33.9 kb in size which is bigger than GIF but is far better in quality as it does not appear as grainy.

JPEG – JPEG stands for Joint Photographic Experts Group. This is used most commonly for photographs due to its ability to store around 16million colours. It does however use lossy compression meaning some quality is lost. The compression however makes changes in colour which the human eye cannot detect. This image is 26.4kb in size which is bigger in size than the GIF image but not as large as the PNG.

Revision Questions

1 ASCII vs UNICODE

a) An advantage of Unicode over ASCII is that it can store multiple lanuages where as ASCII only stores English characters. This is because ASCII only uses 7bits to represent each character compared to UNICODE which uses 16 bits.

b) A disadvantage of UNICODE over ASCII is that it takes up twice as much space when storing.

2) Representing negative numbers using two’s complement

72 represented as a positive number would look like this

01001000

When using twos complement to represent itas a negative it would look like this

10111000

Increasing the width of the data bus enhances system performance as it means more data can be carried at once making tasks faster and so increases system performance.

4) Control lines

Two control lines are reset and clock.

      

5) Printer spooler

A printer spooler works by sending data from the computers backing storage to the printer in order to allow the user to carry out othertasks on the computer.

Vector graphics

Vector graphics are made up of lines and shapes rather than pixels like in a bitmap image.

Different attributes about these shapes are stored for example the colour, the coordinates, the line thickness or the fill colour.

An advantage of Vector graphics is that they have a much smaller file size than bitmap graphics.

This is because bitmap images have to store information about each individual pixel whereas vector graphics only store attributes about each shape or line.

For creating Vector graphics draw programmes such as draw plus are used. Whereas for creating a bitmap graphic paint programmes such as microsoft paint are used.

            

A disadvantage of Vector graphics however is that individual pixels cannot be changed. This means only the whole shape can be edited not just one small part of it.

Another advantage of vector graphics is that they are scaleable. This is an advantage as it means if the image needs to be enlarged then no quality is lost. When a bitmap image is enlarged then the image becomes more pixelated causing the image to appear blurry.

Audio technical terms

Clipping – This is when distortion of the sound is created because the output hardware is trying to represent a sound which is outwith its capability.

Stereo – This is when two tracks are used separately one is sent through one channel the other track is sent through the other channel. Therefore it gives an effect of live music.

Surround sound – This is when a sound is said to be all around the listener.

Fade – This is when audio gets gradually quieter before slowly disappearing

Bitmapped graphics – Technical terms

Dithering – This is when patterns of dots are changed to make it look as if there are more colours than what they actually are. Dithering helps to make images with few colours appear less blocky however they can appear more grainy instead.

 

Anti- aliasing – This is a technique used to smooth out edges which appear jagged when seen on low quality output devices such as monitors.

Resampling – This is when the amount of pixels in an image is changed. Resampling can change both the resolution of the image and the size of the image depending on whether the amount of pixels is increased or decreased.

The processor

The processor is the main part inside a computer as it links to many other parts. For example data is sent between the processor and backing storage so that when a computer is switched off no data is lost.  

The Processor consists of many different parts such as Registers, ALU, Control Unit, Control Bus, Address Bus, Data Bus.All these different parts do different jobs within the processor.

Registers – These are used as temporary storage locations for data that is being processed. They are also used for when instructions are being carried out. They can also hold addresses of mmory locations to be accessed.

ALU – This is the arithmetic and Logic unit. This is where calculations are carried out and It  out logical operations such as AND, NOT, OR are performed.

 

The control unit – This part of the processor is where  the fetching and decoding of instructions as well as the execution of the instuctions happens.

The control bus – This consists of several wires each having a separate function. There is a read line, write line, interrupt, clock and reset. Each one of these does something different.

Address Bus –  The address bus carries information (on which memory location will be used to store the data) to the main memory. Each line only carries one piece of information at a time. The number of wires in this bus determines how many memory locations can be addressed the more wires the more locations.

Data Bus – The data bus carries between the processor and main memory. It is the only bus in which data is carried both ways. This stores data in memory locations and reads it from memory locations. The more wires this bus has the more data that can be carried at one time. The more data carried at once the faster the computer will be.

The fetch and execute cycle is used to execute a program. First of all any relevant data needed to run the programme must be FETCHED and stored in memory until it is required by the processor. It is then retrieved and each individual instruction is then EXECUTED one at a time.

Graphics

There are two different types of graphics bitmap graphics and vector graphics.

Bitmap graphics are made up of thousands of tiny dots called pixels. The number of dots determines the resolution. The more dots/ pixels the higher the resolution meaning the better quality of the image. The less dots/pixels the lower the resolution meaning it is worse quality. Images in which there are few pixels meaning each square can be seen are referred to as pixelated. Bitmap images are represented using binary. The number of bits used to store each colour in an image is known as the bit depth. Bitmap images have a fixed file area and can be edited to pixel level meaning individual colours can be changed. Bitmap images however Have a very large file size and so take up alot of space and making the image bigger causes some quality to be lost.

Vector graphics however are made up using shapes and lines and points. Unlike bitmap graphics however small colour changes cannot be made. It is stored by saving information about the attributes rather than using pixels. Vector graphics have a much samller file size and so do not take up as much space as bitmap graphics. Objects created can be resized and moved around.  Unlike bitmap graphics though the fine details cannot be edited and although they have a smaller file size as more shapes are added the file size increases.

Data Representation

Positive numbers are represented by the binary system. As humans we use a decimal number system which is base 10, however computers use a binary number system which uses only 1 or 0, this is known as base 2. This is used for simplicity for the computer where 0 bits repreents an off voltage and 1bit represents an on voltage. The binary system is worked out in a similar way to decimal. In our systemm we have units tens hundreds thousands etc which is used to represent the value of each number. For example the units column is worked out by 10 to the power of 0 and the tens column by 10 to the power of 1 and the hundreds column ten to the power of 2. Binary works the same but instead of base 10 we use base 2. This is worked out like this : the 1 column is worked out by 2 to the power of 0. The 2 column 2 to the power of 1 and so on. By using these rules we can convert between binary and decimal which is essential for the communication between the computer and the user.

Negative numbers can be represented two ways. The first way is known as signed bit representation. This uses the firstbit to determine whether a number is positive or negative. If the first bit is 0 then the number is positive whereas if the first bit is 1 the number is negative. Using this system however gives a positive and negative value for 0 so although it is a simpler system it is not as efficient. The second way to represent negative numbers is by using Two’s compliment. To work out what a negative number is using this we have to change all the 1 values to 0s and all the 0 values to 1 then add 1. This will give us the negative equivalent of a positive number.

Real numbers are represented using what is known as floating point notation. This method separates the number into two parts the mantissa and the exponent.The mantissa holds the full number with no decimal point and the exponent holds the number of places the point must be moved for it to reach the left most part of the number. The larger the amount of bits in the mantissa the higher the accuracy of the number.

Text is represented in binary by a unique code. ASCII is a widely recognised and agreed code used to represent text. The same code is used for each letter in many countries to keep communication easy. The problem with ASCII however is it only uses 7 bits and so only allows for 128 characters to be represented this is not enough. Then came the invention of extended ASCII which allowed for 8 bits to be used to store 256 characters which was better although still not enough. These codes did not allow for the vast amount of lanuages to be stored for example Japanese, Chinese or Arabic. This is why UNICODE was invented. Unicode uses 16 bits (2bytes) to represent each character which allows 65536 characters to be stored.

Bitmap graphics are also stored using binary. If you have a black and white image there will be only two colours and therefore only one bit is needed because 0 will represent one colour and 1 will represent the other. However most images have lots more colours than that and so more bits are needed. the way to work out how many colours can be stored in each bit is by doing for example 2 to the power of 4 which will tell you how many colours can be represented by 4 bits which would be 16. The number of bits used to represent an individual colour in a pixel is known a the bit depth.

Standard Algorithms

Linear search is one of the Standard Algorithms. This allows the user to perform a search for a number from a list and returns the position of the number in the list. This works by taking the search number and comparing it with the current number. For example if the search number was 4 then a linear search would compare all numbers with 4 until 4 was found and the number of spaces counted until 4 is reached wouldbe the position.

Count occurences is a second standard algorithm used. Count occurences adds up all the times a number appears in a list. Every time the search item is found 1 is added to the total. With this algorithm the total must be assigned to 0 before starting. When it reaches the end of the list the total occurences is displayed.

 

 

Implementation

Implementation is the 3rd stage of the software development process.

At this stage the design gets turned into a computer programme. There are 3 types of programming lanuages:

Event driven – this is when blocks of the programme code are activated when a button is pressed.

Procedural – this is when the code is run from top to bottom and there is a clear start and end point.

Declarative – this is when the programmer declares all facts and rules at the beginning of the program, this allows queries to be performed.

There are 7 characteristics of a completed program, these are :

Correct- If a programme is correct it will meet the software specification which is a document agreed between the client and programmer.

Maintainable – Changes and updates should be able to be made easily and quickly.

Readable – It can be easily understood by other programmers making maintenance easier.

Reliable – it does not have bugs and should produce the correct answer every time it is run.

Portable – It may be adapted to run on different types of computers than what it was created on. For example it should run on laptops and computers.

Efficient – It should not take up more processor time or storage than what is necessary for the size of the programme.

Robust – It shouldnt fail no matter what the user inputs into the programme.

Programming lanuages have 3 different structures these are

Sequence – all lines of code are executed from the beginning to end

Selection – only some lines of code are executed

Iteration – lines of code are repeated in a loop.

There are two types of lanuages a high level lanuage and a low level lanuage.

A high level lanuage is one that is easily understood by humans. It uses words such as  If, Then, Else.

A low level lanuage however is what is understood by the computer this is binary and is often called machine code.